Laboratory techniques frequently require repetitious handling of very small samples of liquids, for example, in the range 1 to 250 microliters. Various pipetting devices are commercially available to simplify these otherwise laborious pipetting procedures. Some of the pipetting devices are described in the prior patent art including U.S. Pat. Nos. 3,606,086; 3,815,790; 3,827,305; 3,918,308; 4,054,062; and 4,084,730. Another commercially available device is illustrated in FIGS. 3 and 4. It includes a disposable, integral capillary and plunger tip assembly wherein the plunger tip is collet attached to an adjustable plunger stroking mechanism carried in the pipette handle to which the capillary is separately attached. In a first mode, the plunger stroking mechanism moves the capillary tip within the capillary for liquid pick-up or dispensing and in a second mode over-travels to permit ejection or attachment of the plunger tip and capillary assembly. A lead screw adjustment permits variation of the plunger stroke with a visual readout for the stroke setting.
Although some of the referenced patented devices use air displacement capillary tips, the device of FIGS. 3 and 4 employs only a positive displacement type capillary and plunger tip with collet-type attachment for the plunger tip and a stroke adjustment which may produce errors in calibration.